Persons in the medical practice, i.e., doctors, nurses and laboratory technicians, are exposed to hypodermic needles which have been used for the injection or withdrawal of fluids into or from persons having various illnesses. Many diseases can be contracted this way, and the present danger of contracting Hepatitis B, Acquired Immune Deficiency Syndrome (AIDS) and other diseases causes a need for extra caution on the part of those health professionals. A used hypodermic syringe needle is a hazard of which the health profession has become more aware since the fairly widespread distribution of these virulent strains. Thus, there is a need to protect health professionals against being scratched or punctured by those needles.
The prior art syringe is described in U.S. Pat. Nos. 5,120,309 and 5,154,698. The prior art syringe includes a barrel having an axis and having a coaxial end wall needle and having a coaxial plunger, a protective shield slidably engaging and mounted on the barrel for covering the needle in one shield position after injecting medication, or for exposing the needle in a second exposed position before injecting medication, and a detent subassembly for temporarily holding the shield in either position.
One problem with the prior art syringe is that the used needle tip is covered by a reversible shield after injecting medication, which can lead to a needle puncture that can cause serious harm.